The National Biomedical ESR Center, established in 1976 at the Medical College of Wisconsin is the largest biomedical ESR facility in th world with balanced separately funded programs of health related research in the major branches of the field: spin labels, transition metals, and free radicals. During the previous five year funding period, two notable advances in Technological Development occurred that form the basis of much of the renewal. Multiquantum ESR spectroscopy, the first advance, has the potential of dramatically changing and improving the basic technology. New approaches to computer-aided ESR, the second advance, including Sensitivity Analysis and Pseudomodulation strengthen the application of modern information theory to ESR spectroscopy. Other developments of the Center also impact on the structure of the proposal including multifrequency ESR, loop gap resonators, and improved microwave bridges. Specifically, five Technological Research and Development projects are proposed: (1) Construction of a state-of-the-art X-band spectrometer with multiquantum capability, (2) Further studies on multiquantum ESR spectroscopy, (3) loop gap resonator design (4) computer-aided ESR and (5) development and application of a rapid-mixing-rapid-scan accessory. The Center has grown during the past five years following its move to a new building and a more than double increase in the number of graduate students. This growth presents new opportunities, and the proposal requests a substantial increase in level of support. The goals of the center are (a) to be innovative in developing new ESR instrumental modalities, (b) to make available at a national level advanced ESR instruments and expertise, and (c) to carry out separately funded health research in selected areas using ESR spectroscopy.